Rapid development of wireless communications has constantly affected habits and behavior patterns of people, and recently, Internet of Things (IoT) service technologies connecting persons and wireless devices anywhere and anytime have been under development. A wireless sensor network (WSN) provides and maintains connectivity among devices and persons, as a core technology for deploying IoT services. However, since devices in a WSN operate in limited computing capability and battery condition, the WSN is frequently damaged due to the change of channel condition, interference, malfunction, and power depletion. In order to deploy a WSN system, devices in the WSN need to be recovered from networking damage through efficient network self-healing.
A cluster-tree structure provides ease of network controllability since a network may be divided in terms of network layer and cluster unit, where a main communication device, referred to an access point (AP), makes network association with a plurality of devices in a parent-child device (node) relationship. A device, referred to a router, may have its child devices, and transmit and receive data to and from its child devices. A device, referred to an end device, cannot have its child devices.
ZigBee widely applied to construction of WSNs may perform network operation while reducing power consumption of devices by means of duty cycling with a super-frame structure in which a parent device synchronously operates with its child devices by periodically transmitting a beacon signal in a beacon-enabled mode, and a signal is transmitted and received during an active period and is not transmitted and received during an inactive period. When a child device does not consecutively receive a beacon signal from its parent device a certain number of times due to link damage between the child device and its parent device, the child device determines itself as an orphan device and performs following network re-association process.
A child device becoming an orphan device sequentially scans available channels to find parent candidate devices (i.e., an AP or routers) nearby, determines information on a set of parent candidate devices using a beacon signal received during the channel scanning, selects a parent candidate device as a device having the lowest network depth in the set of parent candidate devices, and requests the parent candidate device to allocate a new address, thereby re-associating the WSN.
However, since a network self-healing technique of ZigBee does not allow an orphan device having its child devices to make normal packet transmission with its child devices during the network re-association process, an orphan propagation phenomenon, in which the child devices of an orphan device are unable to receive a beacon signal and thus all the child devices may become orphan devices, may occur. Due to the orphan propagation phenomenon, despite link damage at one device of a network, a plurality of devices becoming orphan devices may need to perform network re-association process, which may take long time and large power consumption for the network re-association. Thus, ZigBee may not be able to efficiently handle networking damage frequently occurred in a practical environment.